Method and means for producing a magnetically induced design in a coating containing magnetic particles

ABSTRACT

The invention discloses a device and a method for transferring a predeterminable, high-resolution magnetic design onto a document printed with a magnetic ink, in particular a magnetic optically variable ink. The device comprises a body of a composite permanent-magnetic material, having at least one flat or curved surface engraved with indicia corresponding to the design to be transferred, wherein the said magnetic material is permanently magnetized, preferably in a direction substantially perpendicular to the said surface. The method comprises imprinting or coating a first surface of a sheet or web with a magnetic ink or coating composition, and approaching the imprinted sheet or web to the engraved surface of a body of magnetized composite permanent-magnetic material while the ink is wet, followed by hardening the ink.

FIELD OF INVENTION

The invention is in the field of security document printing. It concernsa novel means for transferring a security design into magnetic ink, inparticular magnetic color-shifting ink, and a method to realize saiddesign.

STATE OF THE ART

Markings exhibiting a viewing-angle dependent light reflection spectrum(“optically variable devices”, OVDs) are used as an efficient anti-copymeans on bank notes and security documents. Among the OVDs, opticallyvariable inks (OVI®; EP 227,423 B1) have acquired a preeminent positionsince their first introduction on currency back in 1987. Such inks areformulated on the basis of optically variable pigment (OVP), a preferredtype of OVP being the flaky thin-film optical interference devicedescribed in U.S. Pat. No. 4,705,300; U.S. Pat. No. 4,705,356; U.S. Pat.No. 4,721,217; U.S. Pat. No. 4,779,898; U.S. Pat. No. 4,930,866; U.S.Pat. No. 5,084,351 and in related disclosures. Other useful types of OVPcomprise the multiply coated particles described in U.S. Pat. No.5,624,486 and U.S. Pat. No. 5,607,504, and the thin film cholesteric(i.e. chiral-nematic) liquid crystal pigments described in U.S. Pat. No.5,807,497 and U.S. Pat. No. 5,824,733.

Optically variable printed features on security documents such as banknotes are aimed primarily for authentication of the document by theunaided human eye, through a checking of the feature's spectralreflection properties, i.e. its color, at two or more different anglesof view, at least at a near-orthogonal and at a near-grazing view. Saidangle-dependent color is a “simple message” of authenticity, whichcannot be reproduced without having access to the source of theoptically variable pigment, and which can rapidly and easily be checkedby the “man on the street”, and this largely independent of his level ofeducation.

In recent times, non-security optically variable pigments and coatingcompositions have increasingly shown up on the open market, freely soldfor the most various applications, especially in the field of decorativearts. Although these non-security optically variable pigments andcoating compositions do not display the same colors and color-shifts asthe optically variable inks used on banknotes, they have neverthelessthe effect of perturbing the “simple message” of authenticity, which wasthe principal trump of the optically variable inks at the moment oftheir introduction to security printing. The “man on the street” willfrom now on need to be educated in distinguishing a genuine opticallyvariable ink on a banknote from a decorative optically variable coating.

The technical problem to be solved in this context is to find anext-generation upgrade for optically variable ink on bank notes andsecurity printing products. This upgrade should fulfill the followingthree requirements:

-   i) It should carry a “simple message” of authenticity which can be    rapidly and easily checked by the “man on the street”, independent    of his level of education;-   ii) It should not be reproducible without having access to the    source of the particular optically variable pigment;-   iii) It should not be under pressure from another potentially large    market or industrial application.

The stated technical problem can be solved by the use of magneticoptically variable pigment in a printing ink, in conjunction with anorientation of the magnetic optically variable pigment particles in theprinting process through the application of appropriate magnetic fields.This solution responds to the three requirement stated above:

-   i) The magnetic orientation of the optically variable pigment in the    ink after printing results in an easily recognizable “magnetic    design” for the “man on the street”, which can only be achieved by    using an on-purpose-manufactured magnetic optically variable    pigment. The optically variable pigments and coating compositions    which are sold for decorative applications are not suited for    magnetic orientation;-   ii) The combination of optically variable and magnetic properties in    a same pigment is not feasible without having access to the    manufacturing of the optically variable pigment;-   iii) The magnetic optically variable pigment is more expensive in    manufacturing than ordinary optically variable pigment, and the    imparting of the magnetic design requires the printing machine to be    equipped with supplementary technology for magnetic orientation. The    optical effect of the magnetic design is furthermore far less    appealing to the decorative market than the optically variable    effect itself. It is thus not expected that magnetic optically    variable inks will ever have any substantial market potential    outside the very field of security printing.

Magnetic optically variable pigments which can be used for theembodiment of the invention have been disclosed in U.S. Pat. No.4,838,648; in EP 686,675 B1; as well as in WO 02/73250 A2 and in WO03/00801 A2; the latter two describe the best suited pigments to solvethe stated technical problem.

Methods and technology for the orientation of magnetic particles incoating compositions have been disclosed in the prior art, noteworthy inU.S. Pat. No. 3,676,273; U.S. Pat. No. 3,791,864; EP 406,667 B1; EP556,449 B1; EP 710,508 A1 and WO 02/90002 A2; the latter being theclosest prior art to the present application. None of these methods hasproved suited, however, for the transfer of a high-resolution magneticpattern in a high-speed printing process.

SUMMARY OF THE INVENTION

The present invention is in particular about a novel way of applyingmagnetic fields for orienting magnetic particles in a printed ink duringthe printing process.

The present invention addresses furthermore the technical problem ofobtaining a customer-specific high-resolution magnetic design on theprinted article in an easy-to-implement and highly reliable way.

It was surprisingly found that a high-resolution magnetic design orimage can be transferred with a simple device to an applied, wet coatingcomposition comprising magnetic or magnetizable particles.

The device for magnetically transferring indicia, such as a design orand image, comprises a body of magnetized permanent-magnetic material,preferably a composite material such as a polymer-bonded composite. Onemagnetized surface of this material serves to transfer indicia, such asa design or image, to a wet coating on a substrate, such as a sheet orweb. The device is characterized in that the surface of said permanentlymagnetized body carries indicia in the form of irregularities of thesurface, particularly deepenings or heightenings. In this context, thesurface may be flat or curved, particularly in a first dimension and notcurved in a second dimension perpendicular to the said first dimension.Furthermore, the transfer surface may be designed to be directly broughtinto contact with the substrate, which may be a sheet or web.

The device, which is preferably magnetized in a direction perpendicularto its surface carrying indicia, transfers the engraved pattern as ahigh-resolution magnetic image onto a sheet or web carrying a layer of afreshly applied and still wet magnetic ink or coating composition, whenthe said sheet of web is approached sufficiently closely to the saidengraved surface. After drying or hardening the so oriented ink orcoating composition, the transferred magnetic image on the imprintedsheet or web remains fixed.

Permanent magnetic fields can be produced by using known compositemagnetic materials. Irregularities in the surface of such a magnetizedpermanent-magnetic body produce sharp changes in the direction andstrength of the resulting magnetic field. Obviously, the irregularitiescan consist of protrusions or heightenings and/or deepenings, such asholes or grooves in various forms. These irregularities may further beproduced by adding material to the surface or by taking off materialfrom the surface of the body. Taking off material can be effectuated,for example, by engraving the permanent magnetic body, as known from theart of making Intaglio plates. Alternatively, a letterpress-type ofengraved body can be realized as well. If a flat surface is required,the body may be leveled or covered by applying an appropriatenon-magnetic material to the surface. For example, the body can becovered by plastic material to achieve a flat and smooth outer surfaceand cover the irregularities of the engraved indicia.

Alternatively, permanent-magnetic material may be applied to the surfacein order to achieve said irregularity. This can be done, for example, byapplying a magnetic material to the surface of the permanent magnet incertain areas, and to cover subsequently the whole surface with anon-magnetic material, such as a plastic.

One of the major advantages of the device according to the invention isthat the indicia to be transferred can be defined at will by anappropriate choice of the engraving. The device can be realized usingany mechanically workable permanent-magnetic material, such aspermanent-magnetic composite materials, comprising a brittle permanentmagnetic powder in a malleable metal- or polymer-matrix. Furthermore,the device can most easily be implemented as an engraving in apolymer-bonded body of permanent-magnetic material (Plastoferrite).

Alternatively, a polymer-bonded magnetic composite material may befilled, in a liquid or pasty state, into a form which has a negative ofthe desired indicia. After hardening of the polymer, the surface of theresulting magnetic body carries the indicia transferred by the form.However, the preferred embodiment of the invention is to provide apre-formed body of magnetic material and to apply the surfaceirregularities, representing indicia, afterwards in accordance with thespecific requirements of use.

A polymer-bonded body of magnetic material, in the context of thepresent disclosure, is a composite material comprising a rubber- orplastic-like polymer as a structural binder, and a permanent-magneticpowder material as an extender or ‘filler’. Preferred polymer bindersinclude rubber-type flexible materials such as nitrile rubber, Nordel®(EPDM hydrocarbon rubber), and Natsyn® (poly-isoprene), as well as Nylon6 (poly-caprolactam), Nylon 12 (poly-laurolactam), polyamide,poly-phenylene sulfide (PPS), epoxy resins, and Hypalon®(chlorosulfonated polyethylene). Preferred permanent magnetic powdermaterials include cobalt, iron and their alloys, chromium dioxide,magnetic oxide spinels, magnetic garnets, magnetic ferrites includingthe hexaferrites such as calcium-, strontium-, and barium-hexaferrite(CaFe₁₂O₁₉, SrFe₁₂O₁₉, BaFe₁₂O₁₉, respectively), alnico alloys,samarium-cobalt (SmCo) alloys, and rare-earth-iron-boron alloys (such asNdFeB), as well as permanent-magnetic chemical derivatives based onthese structure types and mixtures including them. Polymer-bonded bodiesof magnetic materials are obtainable from many different sources, suchas from Group ARNOLD (Plastiform®) or from Materiali Magnetici,Albairate, Milano, IT (Plastoferrite).

The said magnetic powder material can either be magnetically isotropicor magnetically anisotropic. In the case of magnetically anisotropicpowder materials, the magnetic powder particles are preferably orientedin the matrix or binder so as to determine a preferred direction ofmagnetization, chosen perpendicular to the engraved, extended surface ofthe magnetic sheet. Isotropic polymer-bonded bodies of magneticmaterials, in turn, can be magnetized equally well in all directions.

Bodies of permanent-magnetic composite materials advantageously combinethe desirable magnetic properties (high coercivity) of the otherwisebrittle and not well workable ferrite, Alnico, rare-earth or still othermagnets with the desirable mechanical properties (flexibility,machine-ability, shock-resistance) of a malleable metal or a plasticmaterial. The body of a magnetic composite material can be obtained inany desired size and form, e.g. as a thin, flexible plate which can bebent and mechanically worked, e.g. cut to size, using commonly availablemechanical ablation tools and machines, as well as air- or liquid-jetablation tools, or laser ablation tools. The engraving of the body ofcomposite permanent-magnetic material may be achieved by any way andmethod known in the art, by hand-engraving, by mechanical engravingmachines, as well as by computer-controlled engraving stations which,furthermore, may produce the engraving either with the help ofmechanical tools, or with gaseous or liquid jets of abrasives, orthrough laser-ablation, using e.g. CO₂—, Nd-YAG or excimer lasers.

According to the invention, a sheet- or plate-like body of a compositepermanent-magnetic material, preferably an anisotropically oriented one,is engraved and magnetized preferably in a direction substantiallyperpendicular to the engraved surface of the sheet.

Substantially perpendicular, in the context of the present invention,means a direction which is not deviating more than 30° fromperpendicular direction.

According to the invention, user-defined indicia are engraved into atleast one surface of the said body of permanent-magnetic compositematerial. The engraving can hereby take place either before or after themagnetization operation. The engraving must be sufficiently deep, inorder to create a significant perturbation of the magnetic field at thesurface. Said perturbation of the magnetic field, which is due to thelocal lacking of magnetic material, manifests itself in a bending of thefield lines, which, in turn, are able to correspondingly orient magneticparticles in a wet coating composition on a printed item, when thislatter is brought into sufficient proximity of the device, e.g. placedon top of, the engraved magnetic device.

Said engraved and magnetized body may be a flat plate, or, alternativelyand preferred, a cylindrically curved plate, applied around theperiphery of a rotatable cylinder on a printing machine, for thecontinuous transfer of a magnetic design onto printed documents atelevated speed. Said flat or curved plate may further be mounted on anytype of support.

Said engraving in said plate or body may be filled up with a polymer,which may contain fillers. Said filler may be a soft magnetic material,for modifying the magnetic flux at the locations of engraving, or it maybe any other type of magnetic or non-magnetic material, in order tomodify the magnetic field properties, or to simply produce a smoothsurface. The plate or body may additionally be surface-treated forfacilitating the contact with the printed goods, reducing frictionand/or wear and/or electrostatic charging in a high-speed printingapplication.

The invention can be practised on any type of imprintable sheet or webmaterial, in particular on the materials used for producing a bank note,a value paper, an official document, a tax excise stamp, a label, afoil, a thread or a decal. The imprintable sheet or web material mayfurther be of paper or of polymer (such as PE, PP or PVC), and it maycomprise a single layer, as well as a plurality of layers.

The inventors believe that the effect of the engraving onto the magneticfield can be explained as follows (with reference to the magnetic fieldsimulation depicted in FIG. 1 a): A plate-like body ofpermanent-magnetic material P is magnetized in a direction perpendicularto its extended surface, such as to result in a first face being amagnetic North pole (N), and in a second face being a magnetic Southpole (S). The lines of magnetic field, according to the definition,radiate out of the North pole (N) and into the South pole (S). Anengraving is realized in one of the pole regions of the said plate (theNorth pole in the depicted case).

At the location of engraving, magnetic field-generating material ismissing, and the magnetic N-potential at the bottom of the engraving islower than the magnetic N-potential at the unengraved surface. Themagnetic field lines in the vicinity of the engraving bend inconsequence down, such as to point towards the bottom of the engravingwhich is at a lower magnetic N-potential and represents therefore alocal South pole with respect to the unengraved surface. A sharpmagnetic field transition, equivalent to a N-S-N magnetic polearrangement, is thus produced at the location of engraving. In otherwords: The engraving of one pole (e.g. the North pole) of a magnetizedpermanent-magnetic material takes the opposite magnetic polarity (e.g.that of a South pole)!

In an alternative embodiment, and with reference to the magnetic fieldsimulation depicted in FIG. 1 b, the engraving in the permanent-magneticbody may also be filled up with another material. Said filling materialmay e.g. be a polymer having similar mechanical properties as the saidbody of permanent-magnetic composite. Filling up the engraving rendersthe engraved plate a smooth surface again, which is of advantage duringthe printing and magnetic image transfer operations. Said fillingpolymer may furthermore contain an extender, which may be either chosenfrom nonmagnetic materials, such as CaCO₃ or TiO₂, or from magneticmaterials, such as soft-magnetic iron or low-magnetic-remanencematerials. The depicted device is the same as the engravedpermanent-magnetic plate of FIG. 1 a, but additionally having theengraved gap filled with μ=2000 soft-magnetic iron. The magnetic fieldtransition at the engraving is qualitatively the same as in the absenceof an iron filling, albeit somewhat sharper defined due to the fieldconcentration by the soft-magnetic iron.

FIG. 1 c depicts the magnetic field simulation of a device disclosed inthe prior art (WO 02/90002 A2, p. 27-28), wherein a magnetizable die,e.g. a soft-magnetic iron die with a cut-out or relief image on onesurface thereof is exposed to a magnetic field focussed on the die(represented in the figure by an S-N permanent magnet (99) placedunderneath the engraved μ=2000 soft-magnetic iron die). No sharp localN-S-N magnetic field transition is produced across the engraving, butrather only a gradual change in the magnetic field density, which givesrise to the kind of unsharp orientation effects cited in the mentionedprior art. This device of the prior art is thus not capable oftransferring sharp magnetic images, such as a text or a drawing, to amagnetic printing.

The engraved features must be sufficiently large and deep, in order toallow the resulting local magnetic field changes to penetrate throughthe imprinted sheet or web material or through an air gap into themagnetic coating to be oriented. The magnetic dipole far-field,corresponding to the locally produced N-S-N (respectively S-N-S)transitions, decreases noteworthy with the third power of the distance.Typical papers have a thickness of the order of 100 micrometers. Theminimal largeness and deepness of the engraved features, e.g. anengraved line, should preferably exceed the thickness of the said sheetor web. Preferably the size of the engraved features is at least twicethe thickness of the carrier. The engraving can furthermore be of anyprofile; noteworthy triangular, semicircular, or rectangular.Rectangular profiles are preferred, as they allow for a sharp featuredefinition (resolution). Deeper engraving will furthermore result in ahigher local magnetic field change, and is thus a preferred option.

In another aspect, the invention discloses a method for transferringpredeterminable indicia, such as a magnetic design or an image, onto aprinted document. Said method comprises the steps of

-   a) applying a layer of an ink or a coating composition to at least a    part of a first surface of a sheet or web, said ink or coating    composition comprising at least one type of magnetic or magnetizable    particles;-   b) exposing the coated sheet or web of step a), while the applied    ink or coating composition is wet, to the magnetic field at the    surface of a body of a permanent-magnetic material, said body    carrying predeterminable indicia in the form of surface    irregularities, thereby allowing the said magnetic or magnetizable    particles to orient in the said magnetic field;-   c) hardening the ink or coating composition, thereby irreversibly    fixing the orientation of the oriented magnetic particles of step    b);    wherein the body of permanent-magnetic material is permanently    magnetized, the magnetization being preferably oriented in a    direction substantially perpendicular to the indicia-carrying    surface.

The present invention discloses as well a method for continuouslytransferring, on a printing press, predeterminable indicia, such as adesign or an image, onto a printed document, said method comprising thesteps of:

-   a) mounting a thin, plate-like device around a rotatable cylinder,    said plate-like device comprising a body of a permanent-magnetic    material carrying predeterminable indicia in the form of surface    irregularities, preferably a gravure defining a design or an image    on said surface, such that said surface is located at the outer    surface of the cylinder;-   b) imprinting at least a part of a first surface of a sheet or web    with an ink, said ink comprising at least one type of magnetic or    magnetizable particles;-   c) exposing the imprinted sheet or web of step b), while the printed    ink is wet, to the magnetic field at the surface of said body and    allowing the said magnetic or magnetizable particles to orient in    the said field;-   d) hardening the ink, thereby irreversibly fixing the orientation of    the oriented magnetic particles of step c);    wherein the body of permanent-magnetic material of the said    plate-like device is permanently magnetized, the magnetization being    preferably oriented in a direction substantially perpendicular to    the indicia-carrying surface.

The step of exposing the applied ink or coating composition to themagnetic field of the body according to the invention corresponds, inthe context of the present disclosure, to the step of bringing thecoated or imprinted substrate, i.e. the sheet or web, sufficiently closeto the engraved, magnetized surface of the said body. This approachingor bringing close together allows the magnetic particles in the printingor coating layer to orient themselves with respect to the magneticfield. Noteworthy, the sheet or web may practically be brought intomechanical contact with the said magnetized surface of the said body.Alternatively, a tiny air gap, or an intermediate separating layer maybe provided.

In a particularly preferred embodiment, a second surface of the saidsheet or web, opposite to the said imprinted or coated first surface, isapproached to or brought into loosely contact with the engraved surfaceof the body of magnetized composite permanent-magnetic material.

The said body of magnetized composite material is preferably the body ofthe device as described above. In a further aspect of the invention, amethod is claimed for producing the said device, the method comprisingthe steps of:

a) providing a device comprising an unmagnetized body ofpermanent-magnetic material, the body having at least one flat or curvedsurface;

b) creating irregularities on said surface, preferably by engravingpredeterminable indicia into the said surface of the body of step a);

c) permanently magnetizing the engraved body of step b), preferably in adirection substantially perpendicular to the engraved surface.

In a variant, the method for producing the said device comprises thesteps of:

a) providing a device comprising a permanently magnetized body ofpermanent-magnetic material, the body having at least one flat or curvedsurface and being magnetized preferably in a direction substantiallyperpendicular to the said surface;

b) creating irregularities on said surface, preferably by engravingpredeterminable indicia into the said surface of the body of step a).

The said body of permanent-magnetic material is preferably apolymer-bonded composite as already described before. The engraving ofsaid indicia is preferably performed by using ablation tools selectedfrom the group comprising mechanical ablation tools, gaseous or liquidjet ablation tools, and laser ablation tools.

Said ink or coating composition comprising at least one type of magneticparticles is preferably a magnetic optically variable ink, comprising amagnetic optically variable pigment. Magnetic optically variable pigmentuseful to realize the invention comprises a stack of interferencelayers, wherein one of the layers, preferably the central layer,contains a magnetic material. For further details concerning thestructure of magnetic optically variable pigments reference is made tothe documents cited in the introduction, especially to U.S. Pat. No.4,838,648, EP 686,675, WO 02/73250 and WO 03/00801.

The ink or coating composition is furthermore preferably selected fromthe group of liquid inks, comprising screen-printing inks, gravure inksand flexographic inks. Liquid inks have typical viscosity values in therange of 0.1 to 5 Pa*s at 20° C., and allow for an easy orientation ofthe magnetic pigment.

Curing mechanisms for hardening the ink can be based on solvent or waterevaporation, as well as on UV-curing or on hybrid curing mechanismsincluding evaporation of diluents, UV-curing and other reticulationreactions, such as oxypolymerization and crosslinking reactions.

The method according to the present invention allows to realize magneticdesigns in magnetic and magnetic optically variable ink, which achievean unprecedented graphical resolution. It is possible to write, e.g.text in the form of a magnetic design into an optically variable field,printed with a liquid-ink, e.g. a screen-printing ink. Said text mayoptically appear in a kind of relief (3D-effect), although the printingitself remains geometrically flat. The method is preferably used for theproduction of a bank note, a value paper, an official document, a taxexcise stamp, a label, a foil, a thread or a decal; the productsresulting of the application of the herein disclosed method beingfurthermore easily recognizable as such.

DRAWINGS

The invention is now further illustrated with the help of the drawingsand the exemplary embodiments. The figures show:

FIG. 1 magnetic field simulations (realized with the publicly availableprogram Vizimag 2.5, John Stuart Breeteson, 2003):

-   -   a) a cross section with magnetic field lines through a        rectangular engraving in a vertically magnetized        permanent-magnetic plate;    -   b) a cross section through a similar rectangular engraving in a        vertically magnetized permanent-magnetic plate, filled up with        soft-magnetic iron (μ=2000);    -   c) a cross section with magnetic field lines through a similar        rectangular engraving in a soft-magnetic iron plate (μ=2000),        magnetized by an underlying permanent magnet.

FIG. 2 a) an engraved pattern in a Plastoferrite flexible magneticplate, magnetized perpendicular to the sheet extension;

-   -   b) a transferred magnetic pattern into a screen-printed patch of        magenta-to-green optically variable magnetic ink (scale in        centimeters).

FIG. 3 a) an engraved pattern in a Plastoferrite flexible magneticplate, magnetized perpendicular to the sheet extension;

-   -   b) a transferred magnetic pattern into a flexography printed        patch of green-to-blue optically variable magnetic ink (scale in        centimeters).

FIG. 4 a) an engraved pattern in a Plastoferrite flexible magneticplate, magnetized perpendicular to the sheet extension;

-   -   b) a transferred magnetic pattern into an UV-curing        screen-printed patch of soft-magnetic ink (scale in        centimeters).

FIG. 5 a) an engraved pattern in a Plastoferrite flexible magneticplate, magnetized perpendicular to the sheet extension;

-   -   b) a transferred magnetic pattern into a gravure printed patch        of coercive magnetic ink (scale in centimeters).

EXEMPLARY EMBODIMENTS Example 1

A Plastoferrite plate, magnetised in a direction perpendicular to thesurface (model M100.8, Maurer magnetics AG, CH-8627 Grüningen), wasengraved on a computer-controlled mechanical engraving station with textof different sizes (see FIG. 2 a). The characteristics of theseengraving were as follows:

-   Text height and width: form 3 to 7 mm-   Depth of engraving: 150 μm for the smallest characters, up to 250 μm    for the largest-   Line width: from 200 μm for the smallest characters to 800 μm for    the largest

An OVI® silkscreen ink of the following formula, comprising a magneticoptically variable pigment, was prepared: Diethyl ketone 23% Ethyldiglycol 29% Solution Vinyl VMCA (Union Carbide) 22% BYK-053 (BYK)  1%Magnetic Optically Variable Pigment* 25%*magenta-to-green, 7 layers design as disclosed in WO 02/73250:Cr/MgF₂/Al/Fe—Ni/Al/MgF₂Cr. The Fe—Ni alloy was 85% Fe/15% Ni.

The vinyl resin was dissolved in the ketone-glycol solvent prior to theincorporation of the additive and the pigment. The viscosity is adjustedwith the same solvent blend so as to reach the value of 1 Pa·s at 25° C.Supplementary antifoaming agent may be necessary to run the ink oncertain printing presses.

The ink was applied in the form of a screen-printed patch onto astandard coated paper (80 g/m²), and the so imprinted paper was laid,while still wet, onto the engraved magnetic plate described above,exposing the back side of the imprinted paper to the engraved top sideof the magnetic plate. The ink was then dried in situ using a flow ofhot air.

FIG. 2 b shows that the engraved design of the magnetic plate has beentransferred with high resolution into the magnetic optically variableink patch; this latter shows some kind of 3-dimensional effect and aseems to move when the print is looked at from different angles.

Example 2

A Plastoferrite plate (model M201.1, Maurer magnetics AG, CH-8627Grüningen) was magnetised in a direction perpendicular to the surfaceand then engraved on a computer-controlled mechanical engraving stationwith a geometrical design (two pyramids; see FIG. 3 a). Thecharacteristics of the engraving were as follows: Height and width: 1.5× 2.4 cm Depth of engraving: 200 μm Line width: 200 μm

The engraving corresponding to the upper pyramid was filled up with apolymer, so as to result in an even surface of the engraved plate; theengraving corresponding to the lower pyramid was left as such.

An OVI® flexography ink comprising a magnetic optically variable pigmentof the following formula was prepared: Neocryl BT-105 (Avecia) 41.5% Deionised water  18% Dowanol DPM (Dow)   6% AMP-95 ™ (Angus Chemie GmbH)1.5% Neocryl BT-100   7% Tego Foamex 800 (Tego Chemie Service GmbH) 0.5%Aerosil 200 (Degussa) 0.5% Magnetic Optically Variable Pigment*  25%*green-to-blue, 5 layers design, Cr/MgF₂/Ni/MgF₂/Cr as disclosed inpatent US 4,838,648; obtained form FLEX Products Inc., Santa Rosa, CA.

The formula ingredients were dispersed together and the viscosity of theresulting mixture was adjusted with deionised water to reach the valueof 20-40 s DIN4 at 25° C.

The so obtained ink was applied in the form of a patch onto standardsecurity paper (100 g/m²) and the imprinted paper was further processedas described in example 1.

FIG. 3 b shows that the engraved design in the plate has beentransferred into the ink patch with good resolution, which remainssubstantially unchanged by the filling of the engraving with a polymer.

Example 3

A Plasto-ferrite plate as used in example 1 was engraved on acomputer-controlled mechanical engraving station with text (see FIG. 4a). The characteristics of the engraving were as follows: Text heightand width: 7 mm Depth of engraving: 250 μm Line width: 300 μm

An UV drying soft-magnetic screen ink without optically variableproperties was prepared according to the following formula and knownprocedures: Epoxyacrylate oligomer 37.5%   Trimethylolpropanetriacrylate monomer 14%  Tripropyleneglycol diacrylate monomer 14% Genorad 16 (Rahn) 1% Fine iron powder 25%  Aerosil 200 (Degussa-Heuls)1% Irgacure 500 (CIBA) 6% Genocure EPD (Rahn) 2%

A patch of the ink was screen-printed on a white PVC support (100 g/m²)and the imprinted support was processed as described in example 1,except that the ink was dried in situ using an UV-radiation curing unit.

FIG. 4 b shows that again, the design engraved in the plate has beentransferred to the soft-magnetic ink patch; the latter shows a3-dimensional effect and a seems to move when the print is looked atfrom different angles.

Example 4

A Plasto-ferrite plate as used in example 1 was engraved on acomputer-controlled mechanical engraving station with a hollow circle.In its centre a similar motif of a smaller diameter was deeper engraved(see FIG. 5 a). The characteristics of the engraving were the following:First circles diameters: 2 and 1.2 cm Depth of engraving of the firstdisc: 150 μm Second circles diameters: 1.5 and 0.7 cm Depth of engravingof the second disc: 250 μm

A coercive magnetic gravure ink was prepared according to the followingformula, and using known procedures: Ethanol 25% Ethyl acetate 25%Dicyclohexylphtalate (Unimoll 66, Bayer)  5% Fumaric acid modified rosin(ERKAMAR 3270, Robert Kraemer  5% GmbH & Co) Polyvinylbutyral resin(Pioloform BN18, Wacker-Chemie 13% GmbH) Magnetic pigment 345 BASF 15%Ethanol  4% Ethyl acetate  8%

The resins were dissolved in the solvents prior to the incorporation ofthe pigment. The viscosity was adjusted with solvent blend to reach thevalue of 20-40 s DIN4 at 25° C.

The ink was applied in the form of a patch on a standard security paper(100 g/m²) and the imprinted paper was further processed as described inexample 1.

FIG. 5 b shows that the design engraved in the plate has even here beentransferred to the ink patch; the latter shows a 3-dimensional effectand a seems to move when the print is looked at from different angles.

1-21. (canceled)
 22. A device for magnetically transferring indicia to awet coating composition applied to a substrate, said coating compositioncomprising at least one type of magnetic or magnetizable particles, andsaid device comprising a body of permanent-magnetic material, the saidmagnetic material is permanently magnetized in a direction substantiallyperpendicular to a surface of said body, characterized in that the saidsurface of said body carries indicia in the form of engravings, causingperturbations of its magnetic field, and the said body is either a flatplate or a cylindrically curved plate.
 23. The device according to claim22, wherein said indicia is a design or an image.
 24. The deviceaccording to claim 22, wherein said substrate is a sheet or a web. 25.The device according to claim 22, wherein said body is mounted on arotatable cylinder on a printing machine.
 26. The device according toclaim 22, wherein the body of permanent-magnetic material is apolymer-bonded composite which comprises a macromolecular polymer and apermanent-magnetic powder, said magnetic powder being selected from thegroup of magnetic materials consisting of cobalt, iron, and theiralloys, chromium dioxide, magnetic oxide spinels, magnetic garnets,magnetic ferrites including magnetic hexaferrites, alnico alloys,samarium-cobalt alloys, and rare-earth-ironboron alloys.
 27. The deviceaccording to claim 22, wherein said body is mounted on a support. 28.The device according to claim 22, wherein said surface is covered with anon-magnetic material.
 29. The device according to claim 28, whereinsaid material preferably fills up said engravings in said body.
 30. Thedevice according to claim 22, wherein said engravings in said body arefilled up with a magnetic material.
 31. The device according to claim22, wherein said surface is surface-treated, enabling a reduction offriction resistance and/or wear.
 32. A method for magneticallytransferring predeterminable indicia onto a printed document, comprisingthe steps of a) applying a layer of an ink or a coating composition toat least a part of a first surface of a sheet or web, said ink orcoating composition comprising at least one type of magnetic ormagnetizable particles; b) exposing the coated sheet or web of step a),while the applied ink or coating composition is wet, to the magneticfield at the surface of a body of permanent-magnetic material, said bodybeing either a flat plate, or a cylindrically curved plate, and saidsurface of said body carrying predeterminable indicia in the form ofengravings, thereby allowing the said magnetic or magnetizable particlesto orient in the said magnetic field; and c) hardening the ink orcoating composition, thereby irreversibly fixing the orientation of theoriented magnetic particles of step b); wherein the body ofpermanent-magnetic material is permanently magnetized in a directionsubstantially perpendicular to the said indicia-carrying surface of saidbody and said engraved indicia in said surface cause perturbations ofsaid magnetic field.
 33. The method according to claim 32, wherein saidindicia is a design or an image.
 34. The device according to claim 32,wherein said body is mounted on a rotatable cylinder on a printingmachine.
 35. The method according to claim 32, wherein a second surfaceof the said sheet or web, opposite to the said imprinted or coated firstsurface, is exposed to the said magnetic field of the indicia-carryingsurface of the body of magnetized permanentmagnetic material.
 36. Themethod according to claim 32, wherein the said body ofpermanent-magnetic material is a polymer-bonded composite whichcomprises a macromolecular polymer and a permanentmagnetic powder,wherein the magnetic powder is selected from the group of magneticmaterials consisting of cobalt, iron, and their alloys, chromiumdioxide, magnetic oxide spinels, magnetic garnets, magnetic ferritesincluding magnetic hexaferrites, alnico alloys, samarium-cobalt alloys,and rare-earth-iron-boron alloys.
 37. The method according to claim 32,wherein the said surface of the said device is surface-treated for thereduction of friction resistance and/or wear.
 38. The method accordingto claim 32, wherein the said engraving in the said surface is filled upwith a magnetic or a non-magnetic material.
 39. The method according toclaim 32, wherein the ink or coating composition is selected from thegroup of inks consisting of screen-printing inks, gravure inks, andflexographic inks.
 40. The method according to claim 32, wherein thesaid at least one type of magnetic particles is a magnetic opticallyvariable pigment.
 41. The method according to claim 32, wherein the saidsheet or web is used for the production of a bank note, a value paper,an official document, a tax excise stamp, a label, a foil, a thread or adecal.
 42. A method for continuously magnetically transferring, on aprinting press, predeterminable indicia onto a printed document,comprising the steps of a) mounting a thin, plate-like device around arotatable cylinder, said plate-like device comprising a body of apermanent-magnetic material carrying predeterminable indicia in the formof engravings at its surface, such that the said engraved surface islocated at the outer surface of the cylinder; b) imprinting at leastpart of a first surface of a sheet or web with an ink, said inkcomprising at least one type of magnetic or magnetizable particles; c)exposing the imprinted sheet or web of step b), while the printed ink iswet, to the magnetic field at the said indicia-carrying surface of saidbody thereby allowing the said magnetic or magnetizable particles toorient in the said magnetic field; and d) hardening the ink, therebyirreversibly fixing the orientation of the oriented magnetic particlesof step c); wherein the body of permanent-magnetic material ispermanently magnetized in a direction substantially perpendicular to thesaid indicia-carrying surface of said body, and said engraved indicia insaid surface cause perturbations of said magnetic field.
 43. The methodaccording to claim 42, wherein said indicia is a design or an image. 44.The method according to claim 42, wherein a second surface of the saidsheet or web, opposite to the said imprinted or coated first surface, isexposed to the said magnetic field of the indicia-carrying surface ofthe body of magnetized permanent-magnetic material.
 45. The methodaccording to claim 42, wherein the said body of permanent-magneticmaterial is a polymer-bonded composite which comprises a macromolecularpolymer and a permanent-magnetic powder, wherein the magnetic powder isselected from the group of magnetic materials consisting of cobalt,iron, and their alloys, chromium dioxide, magnetic oxide spinels,magnetic garnets, magnetic ferrites including magnetic hexaferrites,alnico alloys, samarium-cobalt alloys, and rare-earth-iron-boron alloys.46. The method according to claim 42, wherein the said surface of thesaid device is surface treated for the reduction of friction resistanceand/or wear.
 47. The method according to claim 42, wherein the saidengraving in the said surface is filled up with a magnetic or anon-magnetic material.
 48. The method according to claim 42, wherein theink or coating composition is selected from the group of inks consistingof screen-printing inks, gravure inks, and flexographic inks.
 49. Themethod according to claim 42, wherein the said at least one type ofmagnetic particles is a magnetic optically variable pigment.
 50. Themethod according to claim 42, wherein the said sheet or web is used forthe production of a bank note, a value paper, an official document, atax excise stamp, a label, a foil, a thread or a decal.
 51. Use of adevice, comprising a body of permanently magnetized magnetic materialhaving a surface carrying indicia in the form of engravings, for themagnetically induced transfer of said indicia to a wet coating layerapplied on a sheet or web, wherein the said body is permanentlymagnetized in a direction substantially perpendicular to the saidindicia-carrying surface of said body, and said engraved indicia in saidsurface cause perturbations of said magnetic field, and wherein thecoating layer comprises at least one type of magnetic optically variablepigment.
 52. Printed product, comprising at least one coating layer,said coating layer further comprising at least one type of magneticoptically variable pigment particles, characterized in that indicia areembodied in said coating layer through a selective orientation of saidmagnetic optically variable pigment particles, as the result of anexposure of said coating layer to the magnetic field at the surface of adevice according to claim 22 while said coating layer is wet, followedby hardening said coating layer.
 53. Printed product according to claim52, wherein said product is a bank note, a value paper, an officialdocument, a tax excise stamp, a label, a foil, a thread, or a decal. 54.A method for producing a device according to claim 22, comprising thesteps of: a) providing a device comprising an unmagnetized body ofpermanent-magnetic material, the body having at least one flat orcylindrically curved surface; b) engraving predeterminable indicia intothe said surface of the body of step a); and c) permanently magnetizingthe engraved body of step b) in a direction substantially perpendicularto the indicia-carrying surface.
 55. A method for producing a deviceaccording to claim 54, wherein the said body of permanent-magneticmaterial is a polymer-bonded composite, which comprises a macromolecularpolymer and a permanent-magnetic powder, wherein the magnetic powder isselected from the group of magnetic materials consisting of cobalt,iron, and their alloys, chromium dioxide, magnetic oxide spinels,magnetic garnets, magnetic ferrites including magnetic hexaferrites,alnico alloys, samarium-cobalt alloys, and rare-earth-iron-boron alloys.56. A method for producing a device according to claim 55, wherein saidengraving of indicia is performed by a tool selected from the groupconsisting of mechanical ablation tools, gaseous-jet ablation tools,liquid-jet ablation tools, and laser ablation tools.
 57. A method forproducing a device according to claim 22, comprising the steps of: a)providing a device comprising a permanently magnetized body ofpermanent-magnetic material, the body having at least one flat orcylindrically curved surface, and being magnetized in a directionsubstantially perpendicular to the said surface; and b) engravingpredeterminable indicia into the said surface of the body of step a).58. A method for producing a device according to claim 57, wherein thesaid body of permanent-magnetic material is a polymer-bonded composite,which comprises a macromolecular polymer and a permanent-magneticpowder, wherein the magnetic powder is selected from the group ofmagnetic materials consisting of cobalt, iron, and their alloys,chromium dioxide, magnetic oxide spinels, magnetic garnets, magneticferrites including magnetic hexaferrites, alnico alloys, samarium-cobaltalloys, and rare-earth-iron-boron alloys.
 59. A method for producing adevice according to claim 58, wherein said engraving of indicia isperformed by a tool selected from the group consisting of mechanicalablation tools, gaseous-jet ablation tools, liquid-jet ablation tools,and laser ablation tools.